Flight control system



July 24, 1951 R. J. KUTzLl-:R

FLIGHT CONTROL SYSTEM Filed May', 1946 NERA/5 fm wg Patented July 24, 19;.51

2,561,873 FLIGHT CONTROL SYSTEM Robert J. Kutzler, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application May 3, 194s, serial No. 666,894'

(o1. afm- 77) 6 Claims.

This invention concerns an improved flight control system for an aircraft.

An object of this invention is to provide an improved automatic or manually controlled operating means for a control surface of an aircraft in flight.

A further object of this invention is to provide an improved automatic or manually controlled operating means for a control surface of an aircraft in flight in which a control signal as determined by a deviation responsive means or by a manually operated means and which signal is effective to cause movement of an aircraft about an axis, is modified by an additional control signal.

A further object of this invention is to provide an improved automatic or manually controlled operating means for a control surface of an aircraft in flight in which a signal as determined by a deviation responsive means in response to movement of an aircraft or by a manually operated means and which signal is effective to cause movement of an aircraft about an axis, is qualified by an additional signal which is a function of any movement of said aircraft about said axis.

A further object of this invention is to provide an improved automatic or manually controlled operating means for a control surface of an aircraft in fiight in which a control signal as determined by a deviation responsive means or by a manually operable means and which signal is effective to cause movement of an aircraft about an axis, is qualified by an additional signal which is a time function of any movement of said aircraft about said axis. A further object of this invention is to provide a flight control system for an aircraft in which a first electrical signal which is manually selected is utilized to control operation of a control surface of the aircraft and a second electrical signal which is a time function of any movement of the aircraft about an axis is added to said first signal to also control operation of the control surface.

A further object of this invention is to incorporate a rate gyroscope in a flight control apparatus having manually or automatically operated control means. Said apparatus comprises a series of connected networks which are affected by the operation of the control means and the rate gyroscope, the networks governing the operation of a control surface actuating means.

The single gure is a schematic view of a, portion of a flight control system.

This invention is concerned primarily with the control of an airplane about its turn axis. The control of the aircraft about the turn axis is effected by the operation of the rudder and ailerons, not shown. The rudder is operated by means of cables I0 which lead from a cable drum II. The cable drum is driven from a motor I2`. The motor I2 may be of any conventional type capable of being reversibly controlled by the output of an amplifier. The motor is connected to the output of an amplifier I4 through leads I3. The amplifier I4 is of any suitable type which is capable of supplying to an output circuit a voltage the phase relationship of which to the phase of a standard source of line voltage is dependent upon and reversible with the signal voltage supplied to the amplifier. The amplifier and motor means for operating the control surfaces may be of the type disclosed in application Ser. No. 447,989, filed June 22, 1942.

The signal for controlling the amplifier I4 is derived from several series connected impedance networks 20, 4l), ECI, 80, and 95. 'I'he signal circuit for amplifier I4 extends from input terminal 32a of the amplifier I4 to wiper 3l, impedance network 20, lead 35, wiper 4I impedance network 4B, lead 43, lead 44, wiper 59, impedance network 60, lead 10, wiper 1I, impedance network 80, lead 13, lead SI, wiper 92, impedance network 95, to ground IUI and to ground |02 of amplifier I4.

The impedance network 20 is in the form of a Wheatstone bridge, two legs of which are formed by a resistor 2l having its ends connected through leads 23 and 24 to the ends of the secondary 22 of the transformer 26, the primary of which is indicated by the reference numeral |00. Since in. all. of the impedance networks the secondaries may have a common primary, the .primaries of the several impedance networks are indicated by the same reference character IUD. The primary Illll may be connected to an inverter, not shown, which forms a source of supply for the primaries. The other two legs of the bridge are formed by a resistor 25 which has its ends connected respectively to the ends of the secondary 22. A wiper 28 is positioned to engage the surface of resistor 25. A wiper 21 is positioned to engage the surface of resistor 2l. A connection 29 from wiper 2l leads to one end of a resistor 30, the other end of resistor 30 being connected through a lead 32 to a center tap 33 of secondary 22. The wiper 3l is positioned to engage the surface of resistor 30.

If Wiper 3| be positioned at the end of resistor 3l! which connects with lead 29, the impedance network 2U with respect to amplifier I4 is in the form of a conventional Wheatstone bridge. If

the voltage drop along resistor' 2i hetween wiper 21 and lead Zl differs from the corresponding voltage drop along resistor '125 `oetween wiper 28 and lead 23, a voltage signal appears between wipers 21 and 2B. This signal voltage may oe made to disappear by the adjustment of either wiper to equalize the voltage drops. When no signal voltage exists between the wipers 21 and 28, they may be considered as balanced or centered. Wiper 28 may be adjusted by hand. if wiper 2B ce adjusted so that a voltage signal appears across wipers 28 and 21, wiper 21 may in turn be adjusted until no signal appears across the wipers. lt is evident, therefore, that the respective positions ol the wipers along their resistors with no signal voltage between them may be varied as desired. Resistor and wiper Rt are therefore designated the centering means since they may be manually adjusted to vary the position of no signal voltage or, as stated above, the balance or center position.

The function or the network 2Q with respect to amplier |4 and motor i2 is to provide means to adjust the normal position or the rudder or the aircraft. If the aircraft in. flight is continually moving off its desired direction of movement, the rudder may be in improper position. To change this normal rudder position, the ainplier I4 is controlled by a network 211; the other networks are assumed to be in balanced condition. 1n a half cycle the left ends of resistors 2|, 25 may be assumed neg `tive as indicates* with respect to their right ends. l wiper Elfi moved toward the lelt lroni its balance position, wiper 21 and wiper Iii which is positioned at the junction ci' resistor 36 and lead 28 will be positive with respect to wiper 28 and thereoy set up a signal between them and wiper 2B of a predetermined polarity. Since wiper 21S connected through the o .ier networlis to ground and wipers 21 and 3| are connected to the amplifier input signal ol? a predetermined phase dependent upon the direction ci unbalance will be applied to amplifier I4. Ampliiier |4l thereupon causes motor i2 to operate in a direction dependent upon the phase of said signal. Motor I2 is connected through a followup means |33 to wiper 21 as well as to cable drum When motor i2 operates it positions the cables leading to the rudder as well as operates the follow-up means iil to position wiper 21 until no signal voltage is derived. The operation oi" wiper 28 therefore is used to position the rudder either to the right or to the leit as desired.

If the wiper 3| be moved from the end of resistor 33 which joins lead 2.9 toward the end of resistor which joins lead the effect or inipedance network on amplifier I4 is modified from the condition originally stated. The potential on wiper 3| and t potential on wiper 28 which is connected to ground |il| and ground |02 of amplier i4 may he measured with respect to the voltage of the center tap 33 ci secondary 22. If wipers 21 and 28 be moved the same amount from their electrical center or balance position on their respective resistors 2| and 25, the amplifier lil would not be in a balanced or inoperative condition because the potential of wiper I5 is not that of wiper 21 but is different therefrom due to the voltage drop through a portion of resistor Wiper 3| which. is connected to amplifier input Bic and wiper 28 which is connected to ampliiier ground therefore would not be at a balanced potential and the amplifier |4, due to this imbalance between wipers 3| 28, would operate. In order that wiper 3| be. at

the same potential as wiper 28, it is necessary to move wiper 21 a different amount from its electrical center than wiper 28 is displaced from its electrical center. It is therefore seen that if iper 28 is moved a given amount from its electrical center the amount of movement given to wiper 21 to set up a balance between the voltages on wipers 3| and 26 to render the amplifier |4 inoperative dilers from that movement given to wiper 28. The amount of movement given to wiper 21 to effect balance of wipers 3| and 28 depends upon the position which wiper 3| is given with respect to the ends of resistor 3U. Resistor 2| and wiper 21 are designated the rebalance potentiometer for the impedance network 20. It is seen that the amount of movement given wiper E1 to reste e ampliiier I4 to non-operating condition may be varied by the movement of wiper 3| along resistor 30. The rudder is driventhrough motor l2 whenever wiper 21 is driven. Consequently, the amount of rudder movement given until rebalance is effected by movement of wiper 21 may be varied through the adjustment of wiper 3|. Resistor 3G and wiper 3| are therefore designated the ratio means since they may be used to vary the amount of movement given to the rudder for any given signal arising out of the displacement of wiper 28 from its electrical center on resistor 25.

While the ratio resistor 30 and its wiper 3| have been described with respect to the voltage signal set up between wipers 28 and 21, it should be noted that such ratio effect may be applied toany voltage signal derived in the other networks. if wipers 21 and 28 of network 20 are at balanced condition and the voltage signal with respect to ground be applied to wiper 28 of impedance network 2B, the network 20 transmits this signal unmodified through lead 29, resistor 30, wiper 3|, to amplifier input 32a. This signal operates ampliiier I4 and causes motor I2` to position wiper 21 to set up an equal but opposing voltage on wiper 21 with respect to the center tap 33 ci secondary 22 as that applied to wiper 28 to` initiate operation. However, the voltage between wiper 21 and the center tap 3B passes through resistor Sii and if wiper 3| be positioned away from the junction of resistor 3|) and conductor 29, the value of the opposing signal is reduced by the voltage drop in resistor 30 between wiper Sl and the junction. Wiper 21 must therefore move a greater amount due to this voltage drop than if wiper 3| were at the junction.

Thus, .it will be seen that the position of wiper 3| on resistor 3G controls the effect of all input signals to the amplifier I4.

Impedance network 29 through its wiper 28 and lead 35 is connected to a wiper 4| of a potentiometer 4|a which forms part of network 40. The resistor 42 of the potentiometer has one end connected to a wiper 5| of network 4|) and its other end connected through a lead 43 to the center tap of the secondary 46 of impedance network 40. The impedance network 40 comprises a potentiometer having a resistor 45 whose ends are connected through leads 48 and 49 to secondary 46 of a transformer 41 having a primary lill. The wiper 5| is positioned for movement over the surface of resistor 45. The wiper 5| is mechanically connected through an operating means t8 to a rate gyro 51. Wiper 5| may be moved along resistor 45 to select positive or negative voltages with respect to the center tap of secondary 46. This difference of potential is applied to resistor 42. Since wiper 4| may be positioned along resistor 42,` it is seen that wiper 4| may select any desired proportion of the difference-of potential existing between wiper 5| and the center tap of the secondary 45. The rate gyro which positions Wiper 5| may be similar to the type disclosed in Patent 2,365,439 issued December'19, 1944, or Patent 2,246,203 issued June 1'7, 1941. In this type of rate gyro, the rotor of the'gyrof is usually mounted on a horizontal axis forrotation within a casing. The casing itself is' generally `supported on a Cardan ring. The Cardanring may in turn be supported on a base by `means of horizontal trunnions extending from the Cardan' ring. The Cardan ring may be biased to a central position by springs which may engage an arm mounted on one of the trunnions. The arm, which is biased through springs to centralpos'ition, may operate the wiper 5| of impedancenetwork 49 through a mechanical connection 58.

*The center tap of secondary 46 of potentiometer 40 is connected through a lead 44 to a wiper 59 of a potentiometer l69. Potentiometer 60 comprises a resistor 6l which has its ends connected through leads 52 and 63 to a secondary 64 lof. the transformer 65. A wiper 59 which may be moved over the surface of resistor 6| to select positive or negative voltages with respect to center 'tap- 69`has an operating connection 66 leading to a deviation responsive means 51. The deviation responsive means 61 may be a magnetic compass, an earth inductor compass, or a directional gyroscope similar to that disclosed in Patent 2104,62? issued January 4, 1938. Such a gyroscope may be designated a two degree of freedomv gyroscope in which the rotor may be mounted'to rotate about a horizontal axis. A supporting means for the rotor in the form of a Cardan ring may be pivoted about a vertical axis. The vertical axis may include an arm Whichis moved when -the craft on which the gyroscope is mounted alters its direction of movement'. l The` arm communicates its motion through a lock 63 and connection 69 to the wiper 59( l The driving connection between the arm o f the gyroscope and the wiper 59 may include a frictionalfclutch,` not shown. The lock 98 when actuated serves to hold one side of the frictional clutch but permits the other side to move under the action ofthe gyroscope. An example of such locklis disclosed in application Ser. No. 447,989, led June 22, 1942.

center tap S9 of impedance network 69 is connected through a lead 10 to a wiper 1| of a potentiometer. The resistor 12 of the potentiometer has its ends connected to awiper B1 of a potentiometer 89 and to the center tap 99 of a secondary 84 of the potentiometer 89. Potentiometer 8|! hasa resistor 8| whose ends are connected through leads 82 and 83 to the secondary 84. The wiper 81 may be moved over the surface of resistor 8| to select positive or negative potentials with respect to the center tap 99. Such potential may be *applied across resistor 12 through leads 14 and 15; and it may be seen that wiper 1| may be positioned along resistor 12 to select any portion of the 'difference of potential arising be tween wiper 81 and center tap 99. Wiper 81 may bepositioned' from vertical gyro S9 through a connection 88. The vertical gyro 89 is of the conventional type having a rotorwhose axis of rota-- tioriis vertical and which is mounted for three degrees of movement. The gyro is so mounted e: upon the aircraft that movement of the aircraft about its roll axis will cause the gyro to transmit movement through connection 88 to wiper 81. Center tap 90 is connected through a lead 9| to a Wiper 92 of a potentiometer 195. The potentiometer has a resistor 93 which has its ends connected throughleads 94 and 96 to va secondary 91 of a transformer 98. The Wiper 92 may be moved along the surface of resistor. 93. by manually operated turn control means |04. The center of resistor 93 is connected to ground. The turn control means |04 which positions wiper 92 also rotates cam |01. Thelcam |91 has a depressed portion |98 and a circular portion |99. The depressed portion |99 receivesa portion of one space contact |||l. The other space contact is connected through a lead ||4to lock 68. The contact ||9 is connected through a battery ||2 to ground. The lock 68 has its return lead |5 connected to ground. It may be seen that whenever turn control |94 is rotated in one directionor the other `a circuit is completed to lock 68 energizing the same.

The ailerons, not shown, are positioned through cables 2| 9 which are connected to a drum 2|I. The .drum 2|| is driven from a motor 2I2. This motor 2 I2 is similar to motor I2. The motor 2|2 is controlled from an amplifier 214 which is similar to amplifier |4. Amplifier 2|4 is controlled through a series of connectedl impedance networks 220, 260, 89, and 95. The control circuit for amplifier 2 |4 is from the input terminal 232e, wiper 23|, impedance network 220, lead 235, impedance networkzil, lead 210, impedance network 89, lead 9|, rimpedance network 95, ground |01, and ground 202 of amplifier 2I4.A

The impedance network 220, like 1network v29, is in the form of a1Wheatstonev bridge. Twolegs of this bridge are formed by a resistor V22| whose ends are connected through leads 223 and 224 to a secondary 222 of a transformer 226. The other two legs of the bridge are formed by a resistor 225 whose ends are connected through leads' 223 and 224 to the ends of secondary 222. vA wiper 22B is positioned to contact the surface of resistor 225. A Wiper 221 may be positioned along the surface of resistor 22|. Wiper` 221 through a connection 229 is connected to a resistor 2.30. The oppositel end of resistor 239 is connected through lead 232 to the center tap 233 ofsecondary 222. A Wiper 23| maybe positioned along the surface of resistor 230. The wiper 23| 'is `connected to the input 232a of amplifier 2| 4.' The other side of the amplifier 2| 4 is connected to ground at 292. The Vmotor 2|2 which is controlled by amplifier 2| 4 has a follow-up connection 202 for positioning wiper 221.l Wiper 228 is connected through a lead 235 to a wiper 259 of an impedance network 250. Impedance network 26D vincludes a potentiometer whose resistor 26| has its ends connected through leads 262 and 263 to the ends of a secondary 264 of a transformer 265. The wiper 259 through an operating connection 266 is connected to the deviation responsive means 261. The center tap 269 of secondary 264 is connected through a lead 219 to wiper 8-1 of impedance network 80. 1

It may be seen that impedance network 220 is similar to impedance network 2|) and functions in controlling amplifier 2 I4' in the manner network 20'controls amplifier |4. Its operation may be obtained from adescription of the operation lof network `2|). Similarly, impedance network 260 is in the form of a potentiometer having its secondary connected to a center tap and is therefore similar to impedance network, 60. Network Zii operates similarly to network B0.

Operation Preliminary adjustment of the apparatus is made when the equipment is installed. These adjustments involve networks 80 and 40. lt may be seen that the turn control potentiometer 95 and the impedance network 80 which is controlled from the vertical gyro 09 are common to the control networks for both the aileron and rudder. While such control is common, it should be noted that the signal applied to control the rudder from network 80 differs from the signal applied t0 control the ailerons. The reason for this intercontrol is clarified by a recital of its function. For example, assuming that the aircraft is in level flight with the networks balanced and that the right wing drops. In such case, the vertical gyro 09 sets up a signal in impedance network 80 which causes the operation of amplifier 2|4 and motor 2|2 to raise the right wing. A portion of this signa1 due to the response of the vertical gyro 89 is also fed through resistor 12 and wiper 1| to the control means for the rudder. The reason for applying the signal to the rudder is that if the right wing' drops, the plane tends to turn to the right and the signal from the vertical gyro serves to control amplifier I4 and motor I2 to apply left rudder to prevent such turning to the right. Resistor 12 and its wiper 1| are often referred to as the skid potentiometer since wiper 1| is positioned to prevent any skidding which might result from such banking of the plane.

With the wiper 1| adjusted as desired over resistor 12 to prevent skidding, the wiper 4| of network 40 is adjusted with respect to resistor 42 so that when the plane is in a coordinated turn the signal applied to the rudder channel from the vertical gyro and the rate gyro just balancesv the signal set up by turn control network S5 which positioned the rudder to initiate the turn.

The turn control knob |04 may be positioned so that wiper 92 of network 95 may provide a signal for either a right or left hand turn` This signal is applied full strength to both the aileron and rudder channels. However, as the plane banks due to the resulting displacement of the aileron, the vertical gyro moves the wiper 81 of network 00. The signal provided by network 8o to the aileron channel is sufficient to balance the signal set up by the turn control knob |04. However, only a portion of the signal generated by network 00 is applied to the rudder channel. The portion selected is determined by the position of wiper 'H along resistor 12. It is the general practice to position wiper 1| along resistor 12 so that substantially half of the voltage required to center the follow-up wiper 21 from servomotor I4 is .derived from the vertical gyro signal into the rudder channel and half of the voltage signal is derived from the rate gyro in network 40. With the adjustments made the apparatus is ready for flight.

It may be stated that the advantages of the rate gyro in the flight control apparatus are at least twofold. One advantage may be ascertained by assuming the apparatus to be without the, rate gyro. It is proposed to have the plane execute a turn by manual control. In such case the wiper 1| would be positioned along resistor 12 so that any signal set up by turn control knob |04 in network 95 and resulting in banking the plane is opposed by an equal signal set up by 8 the operation of vertical gyro 39 in response to the banked position, which is transmitted tothe rudder channel. With such an arrangement. operation of the turn control |04 sets up a signal in the rudder channel and aileron channel of equal strength. The aileron servomotor 2 l2 positions the aileron and also positions its follow-up wiper 221 to set up an equal but opposing signal to that set up by network 95. At the same time. the motor I2 drives the rudder in accordance with the signal input and also drives its follow-up means |03 to position wiper 21 to set up an equal but opposing voltage to the signal input from turn control means |04. The plane responds to the aileron applied and banks. The vertical gyro 89 responds to the bank and sets up a signal equal to and opposing that set up by network 95 from the turn control means |04. This causes the aileron servomotor 212 to position the ailerons in normal or center position. At the same time. the follow-up means from motor 2 l2 positions its follow-up wiper 221 at its electrical center. The signal derived from network due to the movement of vertical gyro 80 is also applied equally to the rudder channel. This causes the motor l2 to drive the rudder to normal position and also centralizes the follow-up wiper 21. It should be noted that the operation of the turn control means |04 also energizes the lock 68 which prevents the transmission of movement from the deviation responsive means to either the aileron or rudder channel. As the plane approaches the desired direction of flight, the turn control means |04 is moved toward normal position. The movement of wiper 02 toward normal position sets up a signal opposite to that which it set up due to its initial movement. The aileron and rudder servos therefore give their respective control surfaces opposite movement from that which was originally applied to them and also displace their wipers from normal position. This opposite aileron tends to cause a lessening in the banking angle of the plane. The lessening of the banking angle causes the vertical gyro signal to become less and again causes the servomotors to center their wipers and control surfaces. However, the displacement of the wiper 81 from its normal position determines the direction of rotation of the servomotors 2|2 and I2 at this time. The signal causes the motors to rotate in such a. direction that the vertical gyro tends to positionthe wiper 81 toward normal position. In other words, the signal arising out of the displacement: of wiper 81 from its normal position causes the motors 2|2 and |2 to position their control surfaces. The position is such as to effect a decrease in the bank angle, and the vertical gyro 8S consequently moves the wiper 81 toward normal position. As wiper 92 continues toward normal position. the servomotors apply rudder and aileron but the vertical gyro acts to cause the servos to center their wipers and control surfaces. The action is continuous until the plane is level.`

The action will now be considered with the rate gyro 51 incorporated in the apparatus and wipers 4| and 1| properly adjusted. It is assumed that the plane is to be turned to the right. The turn control knob |04 is turned to the right thereby displacing wiper 92 of network 95. Such signal derived from network 95 is applied full strength to the aileron and rudder channels. The respective servomotors 2|2 and I2 of the aileron and rudder operating means position their control surfaces.

'would be desirable to continue to maintain rudder until the fplane is actually ina turn. In the operation of the turn control lmeans without the rategyro, the rudder and aileron were centered upon response of the vertical gyro 89 tothebank ofthe plane. The vpresent arrangement is a considerablel improvement over, the turn control `*without a rate gyro since the rudderfis not centered unless theplan'e is actually ina turn. f

' Y The plane goes into a right bank under the Ainfluence of the right aileron. At the same time,

the plane begins to turn under the `eiect. ofthe right rudder.- 'The bank of the plane causes the vertical gyro 89 to respond to this bank and 4'-moves -wiper 81 to'set up a signalfin network A8l] equal to `that initiated vby turn control means |04. The ailerons are therefore centered. Since only a portion ofvthe signal set up in network 80 .by y

themovementof wiper 811isap'pliedto rthe rudder channel, and since i i this `signal isz. less vthan :that

-set up by-turn control means |04, the rudder is not centered/bythe vertical gy-ro signalapplied to the rudder channeh Ifthe plane` is :actually turning, however, the'rategyro sets up 'a' signal on network'40 through the operating linkage 58 adjusting wiper This signal issurlicientxto causethe centeringv of the rudder-andwip'er y21.

However,` it should be noted1that if thesig'nal' is insufficient,` rudder 1 is still-.maintained until the plane'actually goes intothe right turn de,- sired. `This is-a' verydesirableivarrangement in havingfan element which respondsto .the .actual turning ofthe plane control the centering'o'f the rudder'completely. This lis a guarantee that the Vplane is"actually in a turn. As` the plane ap- 'proaches the desired heading; theturrr. control knob |04 is moved toward normal position; :The

verticalgyro has positioned wiper l81 sothatl -it `callsforl left aileron and left rudder. v At .the sarnel time,` the rate gyrofhhas..positoned wiper 5| off-impedance network 40y so.. that the signal setfup by the wiper vdisplacement calls for .-left rudder operation. The aileron and rudder signals vbeingunbalanced due to the return movement of `turn-control |04 are applied'to their respective servomotors 2|2 and l2.` The motorr 2|2 applies left aileron whichdecreases the angley ofy bank Vof theplane.- The rudder motor l2. applies.I left rudder. Ther .plane `continues to. turn under the influence of its banked position.. The application of the left aileron has decreasedl thev angle` of bank Aso that the vertical gyromoves the wiper 81. toward normal position. This causes the servomotor 2 l2 to center the aileron. The further movement of turn control |04 again causes the application of left aileron. The verticall gyro vresponding to decreased bank again causes motor 2 |2 to center the aileron. The action is continu- .ous so that the plane gradually moves toward level position. Themovement toward level position has an elect in the rudder channel similar lto that in the aileron channelzwith the added signal from the rate gyro. If when the plane reaches level position it is not turning, the rate signal also decreases to zero and the rudder and wiper 21 are in neutral position.

lTherate gyro is also of considerable aid in stabilizing a'y plane lfor flight in adesired direc- ".tion. The flight control apparatus is under the :control or` the'directional gyro and the rate gyro .when the plane is stabilized in flight in a particu- .lardirection Thedeviation responsive means 61 will positionv wiperES of network 60 through linkageewhen the night ofthe plane deviates from :adesireddirectlon., At the same time this directional gyro .through its .connection ZEG displaces the. wiper259 of. network 259. Network 260 applies. a signal to the aileron channel. The dis- .fplaeement orwiper 59 of the rudder channel is the same irrespective of the speed of deviation.

ln other.l words, the magnitude of the displacement of wiper 58, is the same whether the deviation be rapid or slow. The amount of movement whichmotor i2 applies to the rudder is dependent upon: the magnitude of thesignal applied to amplier |4. If the .deviation of the plane be abrupt it: is desiredthat a large signal be applied to amplifier I4 so that a large rudder movement willbeobtained quickly. Such large signal can- Lnot be. derived vfrom the deviation responsive network-.68.. lThe rate vgyro 51 through its network ',fiilrsupplements the deviation signal with a veloc- Sitysignal. If the deviation is slow, the velocity signal from network 4i! will be small since the `rate gyro lil/responds to the rate of turning of the aircraft.

c The interrelation betweenv the deviation responsive ,means t1 and the rate gyro 51 therefore becoinescapparent. The rategyro alone could not vbe used to. stabilizethe plane in a desired direcltion.:of flightsince itis not responsive to slow deviations. On thev other hand, the deviation .responsive means El will sense such slow `deviations. :Thecombination of these two gyros therefore effects the desired stabilized direction of night. It is Aalso evident vwhy the verticalgyro iig is involved in the operation of the rudder. In slowdeviations from a desired direction of movement only thedirectional gyro 61 responds to a change. In turning the plane back on its course, it is desired to operate the plane in a coordinated turn. Such turn is .eiectedby the application of rudder and aileron to the airplane to control i vits return tothe desired direction. It is necessary therefore for the deviation responsive means B1 to control the ailerons as well as therudder.y In orderto center the control surfaces after the plane is in the turn, it is necessary to depend on the vvertical gyro to not only centralize the -ailerons butalso to apply a signal to the rudder channelto centralize the rudder.

Thek operation will be considered when the planev is stabilized in a desired .direction only through the deviation responsive means 61 and Awithoutthe rategyro 451. Wipers 4| and 1| are properly. adjusted;i If the plane be blown sharply -to theleft loff its desired heading, the deviation responsivedevice-G1 responds tothe change in heading. The means-.61, lin responding, positions Iwiper. v59 of the'rudder network lill to the right calling for a lright. rudder. At the same.y time, the-means 61 positions wiper 259.0`f network 260 calling `for right aileron. The servomot'orsvrespend-to the-signal and position the aileron and rudder-respectively -forfaright hand turn and displace' their wipers-211,221 from center position -tpbalance the signal input. `The plane now responds to the movement of its aileron and banks. The vertical gyror 89 now responds to the bank and positions wiper. 8l calling forI left aileron and Aalso left rudderJ The'servomotors'in response to the signal from the vertical gyrocenter their respective wipers-'21, v221 and the rudder, and

l1 aileron are therefore centered. The plane now turns under the effect of the right bank Vof the plane. A5 the plane is turning toward the right, the deviation signal becomes less. In other words, wiper 59 moves to the left and wiper 259 moves to the left. Wiper 81, however, is in the position calling for left aileron and left rudder, and its signal exceeds the signal derived from the respective positions of wiper 59 in the rudder channel and wiper 259 in the aileron channel. The servomotors l2 and 2I2 therefore apply left rudder and left aileron. The plane which is in a right bank responds to the left aileron and decreases the value of the right bank. The vertical gyro `therefore moves its wiper 81 slightly to the right from its leftward position. This sets up `an unbalanced signal in the networks causing servos I2, 2I2 to center their wipers and control surfaces. The deviation signal decreases still further as the plane approaches its desired heading. This leaves an unbalance signal under the ycontrol of the position of wiper B1 and this left signal again calls for left aileron and left rudder. Theservomotors apply left aileron and left rudder to decrease the right bank of the plane still further, which again causes centering of servo `wipers and control surfaces. The action is continuous so that when the plane reaches its desired 'heading the plane is level and the rudder and aileron are in center position. In the above recited operatic-n, the value of the rudder displacement was solely proportional to the magnitude of the deviation. The turn is not achieved as quicklyr as it would be were the rudder positioned not only in accordance with the deviation signal but also in `accordance with a velocity signal.

The `operation of the apparatus will be considered when a rate gyro functions with the deviation responsive means in stabilizing an aircraft in a particular direction of flight. In a general analysis of the operation it may be stated that the rate gyro reinforces the signal from the directional gyro in the initial movement of the iplane toward its desired heading. As the plane approaches the desired heading, however, the rate gyro signal is opposed to the deviation signal. The .position of the rudder is determined from the `algebraic sum of the signals derived from the position of the follow-up wiper 21 in its network 2li, the `position 4of the wiper 5| of the rate gyro in its network 48, the position of the wiper 59 from the deviation responsive means in its network 60, and the position of the wiper B1 operated by the vertical vgyro in its network 8|). The algebraic sum of these signals derived from the networks must equal zero. The deviation signal may vary from a large plus value to a zero value. The signal from the rate gyro may be considered plus initially and minus near the end of the .application of the correction. The vertical gyro signal varies from a large negative value to a zero value. The follow-up wiper 21 has a positive or negative value depending upon the alge- `braic sum of the other three values. In other words, at times it may have a plus value and .at times it may have a negative value. In view ofthe fact that the operation is continuous, that is, the voltages are being continually balanced, the values of the signals depart from their initial values. An attempt will be made to set down in detail the operative steps insofar as the operation of four continuously variable interrelated quantities can be set down. Assume that the plane is blown sharply to the left off its i COUI'SE.

l2 The deviation responsive means 61 and `the .rate gyro 51 respond to this abrupt turning of the plane. The directional gyro positions wiper 59 to call for a right rudder. It also `positions wiper 259 to call for a right aileron. Therate gyro also responds and calls for a right Irudder. The servomotor l2 responds to the signal set up by means 61 and by rate gyro 51-and applies right rudder. The servomotor 2l2 responds to the deviation signal and applies .right aileron. The motors also position their vfollow- .up wipers to the left to balance the right signals set up by the deviation responsive means :91 .and the rate gyro 51 in one case and the deviation signal in the other. The application of the right aileron causes the plane totilt. The vertical gyro 89 responds to this tilting of the plane and sets up a signal vcalling for left rudder and left aileron. Since the voltage may be considered Aunbalanced to the left, the amplifiers vcontrol their respective servomotors 212 and I2.

The aileron is centered as is also its follow-up wiper. However, the rudder is not centered because the signal from the rate gyro and the deviation responsive means 61 exceed the value of the rudder signal derived from vertical -gyro 89 and network 8U. Now it should be realized that the value of the deviation is increasing at this time Whereas the value of the rate gyro signal is decreasing. When the effect of the right bank of the plane overcomes that due to that applied from the outside air. the plane begins to turn toward its desired heading. The plane may be said to be in a reverse curve at this time. The plane is in its maximum right bank at this point. When the plane is in such position, the rate gyro signal decreases to zero since the planes rate of turning is changing from a plus value to a minus value through this point.

vAs the plane heads toward its desired direction under the influence of its banked position, the rate .gyro signal opposes the deviation signal. As the deviation signal becomes less, the banked position of the plane as in previous operations described becomes less. Finally, as the plane reaches its desired heading, the aircraft is dying level, the ailerons are in normal position, and the 'aileron networks are in balance condition.

.1f the plane is steady on its course, the rate gyro signal is zero and the rudder is centered and its network is balanced. If the plane is still turning, the rate gyro holds a left rudder to `offset the turning action.

It has now been shown that this invention Aprovides a means for generating a velocity signal. This velocity signal generating means provides a factor which not only provides better stabilized turns of the aircraft which are initiated by hand but also provides an aid to stabilize automatically the direction of night of an aircraft.

I claim as my invention:

l. Control apparatus for an aircraft comprising: two control surface motor means; separate means for controlling the movement of each said -motor means; a plurality of adjustable signal `producing devices; means for combining the signals from said devices and connected to each control means; manual `actuating means adapted ito adjust one device to provide a signal to effect operation of both said motor means; means responsive to the movement of said aircraft about one axis resulting vfrom the operation of one motor means and adapted to adjust a second vdevice to `provide an opposite signal to control 13 the two motor means; and means responsive to the movement of the aircraft about the other axis resulting from the movement of the other control surface to adjust a third device in the control means for said last control surface motor means.

2. Control apparatus for an aircraft having two control surfaces, each of said control` surfaces controlling the movement of said aircraft about one of two respectively perpendicular axes, said apparatus comprising: motor means for positioning each said control surfaces; a plurality of signal voltage producing devices eachv having a part fixed to the aircraft and an adjustable part; a control means for each motor means and responsive to signals from some of said devices; manually actuable means adapted to adjust one device for both control means to effect operation of both said motor means; follow up means operated by each said motor means for adjusting a device for its control means; means responsive to the movement of said aircraft about one axis resulting from the operation of one motor means and adapted to adjust a device for both control means to control both motor means; and means responsive to the movement of the aircraft about the other axis to adjust a device for one control means to control the motor means for the other control surface.

3. Control apparatus for an aircraft having two control surfaces for controlling the aircraft, each said control surface controlling the movement of the aircraft about one of two respectively perpendicular axes, said apparatus comprising: a motor means for positioning each of said control surfaces; individual means for controlling each said motor means and each control means being responsive to a control signal; a plurality of adjustable voltage sources connected in electrical series relation to form two control circuits, one circuit being connected to each control means; manually actuable means for adjusting a first voltage source for each circuit thereby controlling the operation of said motor means; follow up means operated by each said motor means to adjust a voltage source in each circuit for overcoming the effect of the voltage source adjusted by the said manual actuated means; means responsive to the movement of the aircraft about one axis resulting from the operation of one motor means and adapted to adjust a voltage source in each circuit to additionally control both motor means; and means responsive to the movement of the aircraft about said other axis to adjust a voltage source in one circuit to further control the operating means for said other control surface.

4. In apparatus for controlling the direction of for adjusting a third control device in the combining means for said rudder surface motor means.

5. In apparatus for controlling the direction of flight of an aircraft having aileron and rudder control surfaces for positioning said craft about a horizontal axis and vertical axis thereof, said apparatus comprising: motor means for operating said ailerons; motor means for operating said rudder; a separate control means for each motor means; a plurality of adjustable control signal producing devices; means for combining the signals from said devices and connected to each control means; manually actuable means to adjust one device common to each combining means to provide a signal to effect operation of both motor means to cause said craft to turn and bank about said vertical and horizontal axes; craft roll responsive means adapted to adjust a second control device common to each combining means to provide a signal opposed to said manual signal whereby said motor means and the control surfaces are returned toward original positions; means to modify the effect of said second control device adjustment in said rudder combining means to modify the relative position of said ailerons and rudder to coordinate the bank and rate of turn of the craft; and means responsive to rate of movement of said craft about the vertical axis for adjusting a third control device in the combining means for said rudder surface motor means.

6. In apparatus for controlling the direction of ight of an aircraft having aileron and rudder flight of an aircraft having aileron and rudder control surfaces for positioning said craft about a horizontal and vertical axis, said apparatus comprising: motor means for operating said ailerons; motor means for operating said rudder; a separate control means for each motor means; a plurality of adjustable control signal producing devices; means for combining the signals from said devices and connected to manually actuable means `to adjust one device common to each combining means to provide a signal to effect operation of both motor means; craft roll responsive means adapted to adjust a second control device common to each combining means to provide a signal opposed to said manual signal; and means responsive to rate of movement of said craft about the vertical axis each control means;

control surfaces for positioning said craft about a horizontal and vertical axis, said apparatus comprising: motor means for operating said ailerons; motor means for operating said rudder; a separate control means for each motor means; a plurality of adjustable control signal producing devices; means for combining the signals from said devices and connected to each control means; manually actuable means to adjust one device common to each combining means to provide a signal to effect operation of both motor means; craft roll responsive means adapted to adjust va second control device common to each combining means to provide a signal opposed to said manual signal; means responsive to rate of movement of said craft about the vertical axis for adjusting a third control device in the combining means for said rudder surface motor means to stabilize the rate of turn of said craft; and means for modifying the effect of the adjustment of said third control device to vary the rate of turn stabilized.

ROBERT J. KUTZLER..

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

